[AndrewPage]

I'm a complete manual noob, so excuse the dumb question. I have an automatic with paddle shifters.

Why do you downshift to pass on the freeway? Why does downshifting give you more power? Should you upshift right after you pass?

[EJ_3]

You make more torque higher in the RPM band. Jumping to a lower gear put you higher in your RPM band faster than riding the throttle.

[Antetokounmpo]

lol i think you mean you're a car noob

[AndrewPage]

Originally Posted by bk335

lol i think you mean you're a car noob

Probably not inaccurate. I drove a 2004 Honda Pilot before I purchased my 335i. I bought it because its a nice looking car and fast. I won't pretend to know anything about how an engine, clutch, or transmission works, but I want to learn. That's why I'm asking this question.

[mmmnot]

Originally Posted by AndrewPage

Probably not inaccurate. I drove a 2004 Honda Pilot before I purchased my 335i. I bought it because its a nice looking car and fast. I won't pretend to know anything about how an engine, clutch, or transmission works, but I want to learn. That's why I'm asking this question.

No shame in that. We all started somewhere.

It's the people who pretend to know what they talk about that we hate

[Antetokounmpo]

Originally Posted by AndrewPage

Probably not inaccurate. I drove a 2004 Honda Pilot before I purchased my 335i. I bought it because its a nice looking car and fast. I won't pretend to know anything about how an engine, clutch, or transmission works, but I want to learn. That's why I'm asking this question.

Like mmmnot said, nothing wrong with that, just saying. A quick google search would reveal the answer. It's not specific to the e90, nor is it specific to a manual. Why do you think auto transmissions kick down when you floor it?

[gavronm]

Many if not all of your questions are probably answered in this amazing 1936 Chevy promo piece by the Jam Handy Organization. They produced tons of videos like this and they are all incredible in their ability to explain complex mechanical components and for the most part are still 100% relevant when applied to todays cars. Their piece on the differential is also remarkable.

[justpete]

Originally Posted by AndrewPage

I'm a complete manual noob, so excuse the dumb question. I have an automatic with paddle shifters.

Why do you downshift to pass on the freeway? Why does downshifting give you more power? Should you upshift right after you pass?

Downshifting puts more torque to the wheels for higher acceleration at the expense of higher revs. Upshift when you don't need to accelerate any more.

[AndrewPage]

Originally Posted by justpete

Downshifting puts more torque to the wheels for higher acceleration at the expense of higher revs. Upshift when you don't need to accelerate any more.

You say "at the expense of higher revs". Why are higher revs an expense?

[justpete]

Originally Posted by AndrewPage

You say "at the expense of higher revs". Why are higher revs an expense?

Closer to redline and max torque. If you're in an overdrive gear and running at highway speeds you'll not be pushing redline on a downshift, that was just a general comment that downshifting will up the revs.

[Antetokounmpo]

Originally Posted by AndrewPage

You say "at the expense of higher revs". Why are higher revs an expense?

Allow me to explain. Power and torque is what makes your vehicle move. Power is a function of torque. At 5252RPM, 1hp = 1 lb-ft of torque. This is why dyno graphs torque (in lb-ft) and power (hp) lines always cross over at 5252 RPM. The N54 makes peak torque very low in the RPM band, and decreases from there, unlike naturally aspirated engines which have a flatter torque curve that makes the power more linear. As the RPM goes up, the power goes up, to a certain point. On the N54, this is around 5500RPM or so. The torque curve is decreasing at a faster rate than the rpm is increasing, hence why the N54 makes peak power short of redline, around 5500.

Let's put this in perspective. You're cruising at 60mph on the freeway in 6th gear. This is around 2200 RPM give or take. You only have about 100hp down there on a stock N54 since it's so low in the RPM band. You down shift to third and now you're around 4000 RPM. Now you have around 220hp to use, and it'll keep getting higher as you go up the RPM range, up until 5500 RPM and it's start decreasing to redline. So I'm assuming you can figure out that with 220hp you'll be able to accelerate faster than with only 100hp.

[Riceball777]

the best way to understand how gears work is to compare it to a bicycle. I'm going to assume you know how to and have rode a mountain bicycle with gears before. the smaller gears are easier for you to turn the pedals but you can only go so fast in the lower gears because you can only pedal so fast. the bigger gears are harder for you to move them but once you get the pedals moving as fast as the lower gears your going much faster in the higher gears

same thing for a car

[AndrewPage]

Originally Posted by Riceball777

the best way to understand how gears work is to compare it to a bicycle. I'm going to assume you know how to and have rode a mountain bicycle with gears before. the smaller gears are easier for you to turn the pedals but you can only go so fast in the lower gears because you can only pedal so fast. the bigger gears are harder for you to move them but once you get the pedals moving as fast as the lower gears your going much faster in the higher gears

same thing for a car

So the reason you want to upshift at a certain RPM is because the higher gear will be more difficult for the engine to move, so you want to have enough speed so its easier to move and doesn't have to overcome the higher resistance?

Let me know if I've got this straight or if I'm confused. 1st gear is the easiest gear to move and 6th gear is the most difficult (assuming we're talking about a 6 speed)?

When you're traveling along in 6th gear, the engine is putting out a certain number of horsepower. Because its a high gear, that horsepower is turning the transmission a slower speed. So when you switch to a lower gear, the engine is putting out the same amount of power but its less difficult to turn the gear so it spins faster (higher RPM), and you get more power?

That's kind of my understanding right now. Is that correct?

[Antetokounmpo]

Originally Posted by AndrewPage

So the reason you want to upshift at a certain RPM is because the higher gear will be more difficult for the engine to move, so you want to have enough speed so its easier to move and doesn't have to overcome the higher resistance?

Let me know if I've got this straight or if I'm confused. 1st gear is the easiest gear to move and 6th gear is the most difficult (assuming we're talking about a 6 speed)?

When you're traveling along in 6th gear, the engine is putting out a certain number of horsepower. Because its a high gear, that horsepower is turning the transmission a slower speed. So when you switch to a lower gear, the engine is putting out the same amount of power but its less difficult to turn the gear so it spins faster (higher RPM), and you get more power?

That's kind of my understanding right now. Is that correct?

Don't worry about the gear part, that'll confuse you. All you should take away is the transmissions job is to

A. keep the rpm down to improve fuel economy and go faster (can't go past 40 in first gear)

B. put the engine in it's power band (the 335i's power band is 3500-5500rpm) when trying to accelerate quickly.

[Riceball777]

Originally Posted by AndrewPage

So the reason you want to upshift at a certain RPM is because the higher gear will be more difficult for the engine to move, so you want to have enough speed so its easier to move and doesn't have to overcome the higher resistance?

Let me know if I've got this straight or if I'm confused. 1st gear is the easiest gear to move and 6th gear is the most difficult (assuming we're talking about a 6 speed)?

When you're traveling along in 6th gear, the engine is putting out a certain number of horsepower. Because its a high gear, that horsepower is turning the transmission a slower speed. So when you switch to a lower gear, the engine is putting out the same amount of power but its less difficult to turn the gear so it spins faster (higher RPM), and you get more power?

That's kind of my understanding right now. Is that correct?

for the most part you are correct.

[NoSlow5oh]

Originally Posted by AndrewPage

So the reason you want to upshift at a certain RPM is because the higher gear will be more difficult for the engine to move, so you want to have enough speed so its easier to move and doesn't have to overcome the higher resistance?

Let me know if I've got this straight or if I'm confused. 1st gear is the easiest gear to move and 6th gear is the most difficult (assuming we're talking about a 6 speed)?

When you're traveling along in 6th gear, the engine is putting out a certain number of horsepower. Because its a high gear, that horsepower is turning the transmission a slower speed. So when you switch to a lower gear, the engine is putting out the same amount of power but its less difficult to turn the gear so it spins faster (higher RPM), and you get more power?

That's kind of my understanding right now. Is that correct?

Think of the engine and tranny as two different objects working together.
The tranny as a bicycle gearing is a good analogy. You are using the torque multiplier to make it easier to move the car. The engine is an air pump. The faster it revs the more air it can process, and the more power it makes to a certain extent. It starts to lose power after 5500 rpms. Remember that the engine can make 25hp or 300hp at 3000rpms depending on how far you have your foot down, because your foot is opening or closing the valve that allows the air into the engine.

When you are traveling in 6th gear at 60mph, you are about 2200rpms or so, which is not in the sweet spot of power stated in another post above. When you downshift, the engine goes to a lower gear and that lower gear then raises the engine speed to make up for the torque multiplication at the same speed. That increase in engine speed puts you closer to the sweet spot of power which allows you to accelerate quicker.

The reason behind gearing is for fuel efficiency and power, which is to keep the engine in a certain range of rpms to achieve the desired result. This is a generalization and of course not fact for every situation, but I hope this helps.

[motoguy128]

A lower gear ratio gives you more mechanical advantage. Think of trying to dig a hole is hard ground. Pull back on the shovel 6" from the spade, that's like you tallest gear (6th or 8th) now try pulling back at the end of the handle, that's like 1st gear. The problem, is that you had to move maybe 5 times farther to move the spade that same amount.

So applied to an engine, it needs more RPMs. Higher RPM's consume more fuel, more engine wear, less smooth for crusing and at some point, you are limited in maximum speed.

The correct question, is why don;t you just use top gear all the time? Because you would accelerate too slowly.


To compound the matter, your engine makes more power at higher RPM's to a point. It depends on the power curve for that engine. Turbocharged engines generally make more power down low than non turbo engines.

[feuer]

Originally Posted by AndrewPage

Probably not inaccurate. I drove a 2004 Honda Pilot before I purchased my 335i. I bought it because its a nice looking car and fast. I won't pretend to know anything about how an engine, clutch, or transmission works, but I want to learn. That's why I'm asking this question.

Don't you worry about not knowing anything about how engine works.
The n54 will teach pretty quick

[whyzee125]

Think of riding a bike. To go up hills, you downshift and spin your legs faster. Same goes for passing someone, the expense is quicker wear since the engine is spinning faster.

[STR8-6IX]

the fact you are at least asking on here and trying to know more is a good start. like someone else said on here, when you downshift, it puts your rpm into a range where you will have more torque (power) to effectively pass someone without running out of space. generally, you should be in a gear that gives you enough power for the situation, but not more rpm (throttle) then you need. after you pass, generally you shift back into the gear you were in if you dont need the extra power anymore. since you are still learning, i highly recommend you dont mess around with manual mode and just leave it in auto. watch how your transmission reacts to different situations and what gears it likes to use. you will learn everything if you are observant.